Portable oxygen concentrators are well-known. Portable oxygen concentrators process ambient air to separate the nitrogen that is present in the ambient air from the oxygen that is present in the ambient air. A common application for portable oxygen concentrators is in the field of medical use. In medial applications, the oxygen is then delivered to a patient, typically through a nasal cannula.
Portable oxygen concentrators for medical use typically operate using a pressure swing adsorption (PSA) cycle. In the pressure swing adsorption cycle, the portable oxygen concentrator compresses air to between 7 and 40 psig and passes the compressed air through columns known as sieve beds. The sieve beds are filled with a zeolite material that adsorbs nitrogen from the compressed ambient air. The remaining oxygen is passed to the end of the column in a concentration that is typically greater than 90%, whereas ambient oxygen concentration is 20.9%.
After the concentrated oxygen is utilized, the portable oxygen concentrator depressurizes the sieve bed. Depressurization of the sieve bed allows the adsorbed nitrogen to exit the zeolite, and the nitrogen is then purged from the sieve bed.
As a result of the cycle of pressurization, adsorption, depressurization, and purging that occurs within the sieve bed, a single sieve bed cannot provide a continuous stream of oxygen. For this reason, portable oxygen concentrators for medical use typically contain two or more sieve beds. While one or more of the sieve beds are being pressurized, the remaining sieve beds are purged. This provides a constant supply of oxygen to the patient. In addition, in typical portable oxygen concentrators, each sieve bed relies upon one or more of the other sieve beds for proper operation. In particular, purging of a sieve bed is accomplished utilizing some of the product gas from one of the other sieve beds. Thus, a fault in one sieve bed diminishes the performance of the remaining sieve beds.
Ideally, portable oxygen concentrators for medical use are small, lightweight, operate quietly, are capable of at least two hours of continuous battery operation, have a life expectancy of at least two years without failure, and are able to withstand normal indoor and outdoor temperature and humidity conditions. These features provide patients with mobility and independence, and do so with a low cost of ownership.
Ultimately, it is desirable to have an oxygen concentrator that is dependable and requires minimal maintenance. One potential maintenance concern associated with portable oxygen concentrators is degradation of the zeolite material. In particular, the zeolite material will degrade over time if it comes in contact with the liquid water that condenses out of the ambient air during parts of the PSA cycle. It is this liquid water, as opposed to vapor phase water, that causes degradation of the zeolite. Thus, if the PSA cycle is run continuously without employing preservation techniques, the zeolite will degrade such that the oxygen concentration produced by the sieve bed falls below acceptable levels. Depending on the humidity in the ambient air, this level of zeolite degradation could take anywhere from a few days to over a month.
Because portable oxygen concentrators are intended to have at least a two year life expectancy and operate in warm and humid environments, conventional portable oxygen concentrators are designed to prevent degradation of zeolite material. Such designs often significantly increase the complexity of the portable oxygen concentrator. Strategies typically employed include using significantly more zeolite than would be required for dry air, using higher pressures than would be required for dry air, inclusion of sensing electronics to monitor ambient temperature and humidity conditions, as well as structures intended to prevent a liquid water from reaching the zeolite, such as condensers, dryers, and venturi tubes, or use of a vacuum during the purge cycle in an attempt to remove liquid water from the zeolite. As a result of provision of these types of features, portable oxygen concentrators tend to suffer from disadvantages including one or more of added costs, increased size, increased weight, noisiness, or shortened battery operation time.
The zeolite material is inexpensive in comparison to the hardware and software solutions that are been utilized in an effort to prevent the zeolite material from degrading. However, the zeolite material in conventional portable oxygen concentrators is not easily replaceable.
It would be desirable to provide a portable oxygen concentrator having replaceable, disposable sieve beds, thereby obviating the need for hardware and software solutions that are intended to preserve the zeolite material.